JP5590975B2 - Casting tool, casting tool production method and precision casting method - Google Patents

Description

  The present invention relates to a casting tool, a casting tool production method, and a precision casting method.

In general, a precision casting method such as the lost wax method can manufacture parts having difficult shapes and complicated shapes with high dimensional accuracy.
For example, a TiAl-based alloy excellent in specific strength, heat resistance, and corrosion resistance is suitable as a material for various parts of aircraft engines and turbine blades. However, it is harder and more brittle than ordinary metals and alloys, so it can be machined. Have difficulty. The precision casting method described above is widely used for processing such TiAl-based alloys.

  In such a precision casting method, the casting tool is usually formed of ceramics, and a mold formed of alumina or zircon or a crucible formed of alumina or zirconia is often used (for example, Patent Document 1 below). ).

Japanese Patent Laid-Open No. 2004-50198

  However, since the TiAl base alloy is very active and has a high affinity for oxygen, in the prior art, oxygen contained in the ceramic and the TiAl base alloy react (oxidize) (in other words, If the TiAl-based alloy takes away oxygen contained in the ceramic), there is a problem that the surface and the inside of the casting are transformed into oxides, or the oxygen concentration in the TiAl-based alloy becomes high.

  The present invention has been made in consideration of such circumstances. When precision casting is performed with a TiAl-based alloy, the surface and the inside of the cast product are prevented from being transformed into oxides. The object is to prevent the oxygen concentration from increasing.

In order to achieve the above object, the present invention employs the following means.
That is, the casting tool according to the present invention is a casting tool used for precision casting of a TiAl-based alloy, and includes a partition that defines an internal space in which the molten TiAl-based alloy can be stored, and the partition is made of ceramics. and formed base, coupled with oxygen than the ceramic is formed of a strong metal oxides, have a, and a coating layer for coating the base layer in the inner space side, the base layer is 99% or more of zirconia It is formed with .
According to this configuration, the coating layer is formed of a metal oxide having a stronger bond with oxygen than ceramics and has a coating layer that coats the base layer on the inner space side, so that the coating layer is in contact with the molten TiAl-based alloy. It becomes. Since this coating layer is formed of a metal oxide having a stronger bond with oxygen than ceramics, the TiAl-based alloy melt is less likely to react as compared with the base layer formed of ceramics, and the surface of the cast product and It is possible to prevent the inside from being transformed into an oxide and to prevent the oxygen concentration of the TiAl-based alloy from becoming high.

Furthermore, when the temperature of the molten TiAl-based alloy is raised, the TiAl-based alloy becomes more active, but the coating layer makes it difficult for the molten TiAl-based alloy to react. Can be improved.
In addition, a configuration in which the entire partition wall is formed of a metal oxide is also conceivable, but if a slurry is poured into a casting tool manufacturing mold and solidified, the metal oxide precipitates until the solidification is completed. It becomes difficult to produce. However, since the casting tool according to the present invention has a structure in which the ceramic base layer is coated with the metal oxide, the casting tool can be easily manufactured as compared with the case where the entire partition walls are formed with the metal oxide.

The metal oxide may be any one of yttrium oxide, ytterbium oxide, and erbium oxide.
According to this configuration, since the metal oxide is any one of yttrium oxide, ytterbium oxide, and erbium oxide, the coating layer can be formed of a metal oxide having a stronger bond with oxygen. As a result, it is possible to sufficiently prevent the molten TiAl-based alloy from further reacting and increasing the oxygen concentration of the TiAl-based alloy.

The coating layer has a thickness of 0.08 mm or more and 0.48 mm or less.
According to this configuration, since the thickness of the coating layer is 0.08 mm or more and less than 0.48 mm, as described later, when the molten metal is stored in the internal space, the durability time until the coating layer is peeled off is lengthened. can do.

According to the configuration of this, since the base layer is a zirconia coating layer even when the peeled accidentally from the base layer, so that the contact between the molten metal of zirconia and TiAl based alloy. As a result, zirconia, which has a relatively strong bond with oxygen compared to other ceramics, comes into contact with the molten TiAl-based alloy, so that the TiAl-based alloy and the base layer hardly react with each other, and the surface and inside of the cast product are It is possible to suppress the transformation to an oxide and to suppress an increase in the oxygen concentration of the TiAl-based alloy.

A casting tool production method according to the present invention is a casting tool production method according to any one of the above, wherein the slurry is produced by mixing the metal oxide powder and a solvent. And a slurry spraying step of spraying the slurry on the inner space side of the base layer.
According to this configuration, since the slurry manufacturing step and the slurry spraying step are included, the coating layer can be easily formed uniformly and sufficiently thin.

The powder has a particle size of 0.5 μm or more and 3 μm or less.
According to this configuration, since the particle diameter of the powder is 0.5 μm or more, the agglomeration during the drying of the slurry is alleviated and the coating layer is prevented from being softened, and the molten TiAl-based alloy is used. Shrinkage due to sintering at the time of contact can be alleviated and peeling of the coating layer can be suppressed. Moreover, since the particle size of the powder is 3 μm or less, good adhesion of the coating layer to the base layer can be ensured.

The solvent is a non-aqueous solvent that does not contain water.
According to this configuration, since the solvent is a non-aqueous solvent that does not contain water, aggregation of metal oxides can be suppressed as compared with a solvent containing water. That is, metal oxide generally reacts with water and agglomerates immediately. Therefore, if the solvent contains water, the agglomeration proceeds in the slurry production process, which may deteriorate the workability of the slurry spraying process. However, agglomeration is prevented by using a non-aqueous solvent that does not contain water as the solvent, so that the workability of the slurry spraying process can be improved.

The slurry is characterized in that an alcoholic dispersant is added.
According to this configuration, since the alcohol-based dispersant is added to the slurry, it is possible to disperse the metal oxide powder and to improve the workability after the slurry spraying process due to the quick drying property. Can be made.

In addition, the precision casting method according to the present invention is characterized by using any of the above-described casting tools.
According to this configuration, since any one of the above casting tools is used, the surface and the inside of the cast product are transformed into oxides when precision casting is performed using a TiAl-based alloy that is active and has a high affinity for oxygen. It is possible to obtain a cast product having a desired quality by inhibiting the oxygen concentration in the TiAl-based alloy from being increased.

According to the casting tool according to the present invention, when precision casting is performed with a TiAl base alloy, the surface and the inside of the cast product are prevented from being transformed into oxides, and the oxygen concentration in the TiAl base alloy is increased. Can be deterred.
Moreover, according to the casting tool production method of the present invention, the coating layer can be easily made uniform and sufficiently thin.
Further, according to the precision casting method of the present invention, a cast product having a desired quality can be obtained.

It is a schematic structure perspective view of crucible 1 concerning an embodiment of the present invention. It is principal part sectional drawing of the casting_mold | template 10 which concerns on embodiment of this invention. 3 is a cross-sectional view taken along a line II in FIG. 1 (an enlarged view of a main part II in FIG. 2). A graph showing the relationship between the thickness d and the endurance time t of the coating layer 3b according to the embodiment of the present invention, is a graph in the case of forming a coating layer 3b with yttrium oxide (Y 2 _{O 3).} A graph showing the relationship between the thickness d and the endurance time t of the coating layer 3b according to the embodiment of the present invention, is a graph in the case of forming a coating layer 3b with ytterbium oxide (Yb 2 _{O 3).} A graph showing the relationship between the thickness d and the endurance time t of the coating layer 3b according to the embodiment of the present invention, is a graph in the case of forming a coating layer 3b with erbium oxide (Er 2 _{O 3).} It is a figure explaining the manufacturing method of the casting tool which concerns on embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
(Casting tool)
FIG. 1 is a schematic perspective view of a crucible (casting tool) 1 according to an embodiment of the present invention.
As shown in FIG. 1, the crucible 1 is formed in a bottomed cylindrical shape, and an inner space 2 in which a molten TiAl-based alloy can be stored is defined by a partition wall 3.

FIG. 2 is a cross-sectional view of a main part of a mold (casting tool) 10 according to the embodiment of the present invention.
The mold 10 is formed in a rectangular parallelepiped shape, and an internal space 12 in which a molten TiAl-based alloy can be stored is defined by the partition walls 3. The internal space 12 has a plurality of casting spaces having a shape formed corresponding to the shape of the turbine blade.

3 is a cross-sectional view taken along a line II in FIG. 1 (an enlarged view of a main part II in FIG. 2).
As shown in FIG. 3, the partition wall 3 has a base layer 3a formed of ceramic C and a coating layer 3b formed of metal oxide O and covering the base layer 3a on the internal space 2 (12) side. Yes.
The coating layer 3b has a thickness d of 0.08 mm or more and 0.48 mm or less.

As the ceramic C forming the base layer 3a, for example, alumina (Al ₂ O ₃ ) or zirconia (ZrO ₂ ) can be used.
Further, as the metal oxide O that forms the coating layer 3b, for example, any one of yttrium oxide (Y ₂ O ₃ ), ytterbium oxide (Yb ₂ O ₃ ), and erbium oxide (Er ₂ O ₃ ) is used. be able to.
In addition, the manufacturing method of the crucible 1 and the casting_mold | template 10 is explained in full detail later.

Here, the bond strength between the ceramic C and oxygen and the bond strength between the metal oxide O and oxygen will be described.
The oxidation mechanism of the molten TiAl-based alloy is based on the following reaction in which Ti contained in the molten TiAl-based alloy takes away oxygen from the ceramic C of the crucible 1. In the following reaction, M represents an arbitrary element.
1 / 3M ₂ O ₃ + Ti → TiO + 2 / 3M
Table 1 shows each equilibrium constant Kp in the above reaction of ceramic C and metal oxide O. Each equilibrium constant Kp in Table 1 is obtained by an equilibrium calculation based on free energy of generation, and is expressed in logarithm.

As shown in Table 1, compared with alumina (Al ₂ O ₃ ) and zirconia (ZrO ₂ ) of ceramic C, yttrium oxide (Y ₂ O ₃ ), ytterbium oxide (Yb ₂ O ₃ ) of metal oxide O and Erbium oxide (Er ₂ O ₃ ) has a small equilibrium constant Kp. For this reason, it turns out that the molten metal of a TiAl base alloy does not react easily with yttrium oxide, ytterbium oxide, and erbium oxide.

  That is, according to the crucible 1 and the mold 10 described above, the metal layer O is formed of the metal oxide O having a stronger bond with oxygen than the ceramic C, and has the coating layer 3b that coats the base layer 3a on the internal space 2 and 12 side. The coating layer 3b comes into contact with the molten TiAl-based alloy. Since the coating layer 3b is formed of the metal oxide O having a stronger bond with oxygen than the ceramic C, the TiAl-based alloy melt is less likely to react than the base layer 3a formed of the ceramic C. An increase in the oxygen concentration of the TiAl-based alloy can be prevented.

Further, when the temperature of the molten TiAl-based alloy is increased, the TiAl-based alloy becomes more active. However, the presence of the coating layer 3b makes it difficult for the molten TiAl-based alloy to react. Circumstance can be improved.
Moreover, since the slurry 20 of the metal oxide O has poor stability, the entire partition wall 3 (all casting tools) is formed of the metal oxide O by pouring the slurry 20 into a mold and allowing it to solidify for a considerable time. Is difficult,
In addition, a configuration in which the entire partition wall 3 is formed of the metal oxide O is conceivable. However, when the slurry 20 is poured into a casting tool manufacturing mold and solidified, the metal oxide O is precipitated until the solidification is completed. Therefore, it becomes difficult to manufacture the crucible and the mold. On the other hand, according to the crucible 1 and the mold 10, since the base layer 3a of the ceramic C is covered with the metal oxide O, the crucible 1 and the crucible 1 are compared with the case where the entire partition wall 3 is formed of the metal oxide O. Manufacture of the mold 10 can be facilitated.

  Moreover, since the metal oxide O is any one of yttrium oxide, ytterbium oxide, and erbium oxide, the coating layer 3b can be formed with the metal oxide O having a stronger bond with oxygen. As a result, it is possible to prevent the molten TiAl-based alloy from further reacting and to prevent the surface and the inside of the cast product from being transformed into oxides, and to sufficiently prevent the oxygen concentration of the TiAl-based alloy from becoming high. it can.

  Further, since the thickness d of the coating layer 3b is 0.08 mm or more and 0.48 mm or less, the coating layer 3b peels off when molten metal is stored in the internal spaces 2 and 12, as shown in the following experimental results. The endurance time until it can be increased.

4 to 6 are graphs showing the relationship between the thickness d of the coating layer 3b and the durability time t. FIG. 4 shows yttrium oxide (Y ₂ O ₃ ), and FIG. 5 shows ytterbium oxide (Yb ₂ O ₃ ). FIG. 6 shows a graph of erbium oxide (Er ₂ O ₃ ).
In each graph, a plurality of crucibles in which the thickness d of the coating layer 3b is changed to 0.01, 0.10, 0.35, 0.60 mm are prepared, and a molten TiAl-based alloy (1650 ° C.) is stored. Each crucible was left in the furnace, and then the time until bubbling caused by the peeling of the coating layer 3b was measured as the durability time t. Bubbling was visually determined through an observation window provided in the furnace.

  As shown in FIGS. 4 to 6, if the thickness d of the coating layer 3 b is too small or too large, the durability time t of the coating layer 3 b is shortened. Generally, in precision casting, the crucible and the mold are in contact with the TiAl-based alloy for 30 minutes or less, respectively. Therefore, if the thickness d of the coating layer 3b is formed to 0.08 mm or more and 0.48 mm or less, the crucible and the mold It is possible to prevent the coating layer 3b from peeling off during use.

If the base layer 3a is made of 99% or more zirconia, the zirconia and the molten TiAl-based alloy come into contact with each other even when the coating layer 3b is unexpectedly peeled off from the base layer 3a. As a result, zirconia, which has a relatively strong bond with oxygen compared to other ceramics C, comes into contact with the molten TiAl-based alloy (see Table 1), so that the TiAl-based alloy and the base layer 3a are difficult to react. It is possible to inhibit the surface and the inside of the cast product from being transformed into oxides, and to inhibit the oxygen concentration of the TiAl-based alloy from becoming high.
Further, the use of high purity zirconia can further suppress the reaction between the TiAl base alloy and the base layer 3a. Further, the same effect can be obtained when 5% or more of yttrium oxide (Y ₂ O ₃ ), ytterbium oxide (Yb ₂ O ₃ ), or erbium oxide (Er ₂ O ₃ ) is added to zirconia.

  By using such a crucible 1 and the mold 10, the surface and the inside of the cast product are prevented from being transformed into oxides when precision casting is performed using a TiAl-based alloy that is active and has a high affinity for oxygen. At the same time, it is possible to suppress the increase in the oxygen concentration in the TiAl-based alloy and to obtain a cast product having a desired quality.

(Casting tool manufacturing method)
Then, the manufacturing method of the casting tool which concerns on this invention is demonstrated.
FIG. 7 is a diagram for explaining a method for producing a casting tool according to the present invention.
The method for producing a casting tool according to the present invention is to produce a slurry 20 by mixing a powder of metal oxide O and a solvent (slurry production process), and the produced slurry 20 is an internal space in the base layer 3 a of the partition wall 3. The crucible 1 and the mold 10 are obtained by spraying the slurry 20 on the 2nd and 12th sides (slurry spraying step).

  In the slurry manufacturing process, a metal oxide O powder having a particle size of 0.5 μm or more and 3 μm or less is used, and a non-aqueous solvent containing no water is used as a solvent. Further, the slurry 20 is added with an alcohol-based dispersant. At this time, since a non-aqueous solvent containing no water is used as the solvent, the metal oxide O and the solvent do not aggregate without reacting.

In the slurry spraying process, the slurry 20 is sprayed using a spray gun G as shown in FIG. That is, the slurry 20 is sprayed on the inner space 2 side of the base layer 3a on the crucible 1 in which the partition wall (3) is configured only by the base layer 3a.
Similarly, the slurry 20 is sprayed on the inner space 12 side of the base layer 3a on the mold 10 in which the partition wall (3) is configured only by the base layer 3a.

And the slurry 20 sprayed on the base layer 3a is dried, and the crucible 1 and the casting_mold | template 10 are obtained.
During this drying, the dispersant component volatilizes quickly. Further, since the particle diameter of the metal oxide O powder is 0.5 μm or more, aggregation when the slurry 20 is dried is alleviated, and the coating layer 3b is maintained at an appropriate hardness.
Further, since the particle size of the powder is 3 μm or less, the coating layer 3b adheres well to the base layer 3a.

That is, according to the manufacturing method of the casting tool mentioned above, since it has a slurry manufacturing process and a slurry spraying process, the coating layer 3b can be easily made uniform and sufficiently thin.
At this time, since the alcohol-based dispersant is added to the slurry 20, the slurry 20 can be sprayed in a state where the dispersion of the metal oxide O powder in the slurry 20 is well maintained.

  Further, since the particle diameter of the powder is 0.5 μm or more, the aggregation when the slurry 20 dries is relaxed, and the coating layer 3b is prevented from being softened and sintered when contacting the molten metal. The shrinkage due to the above can be alleviated and the peeling of the coating layer 3b can be suppressed. Moreover, since the particle size of the powder is 3 μm or less, good adhesion to the base layer 3a can be ensured.

  In addition, since the solvent is a non-aqueous solvent that does not contain water, the solvent is a non-aqueous solvent that does not contain water, and thus aggregation of the metal oxide O can be suppressed compared to a solvent containing water. That is, since the metal oxide O generally reacts with water and aggregates immediately, if the solvent contains water, the aggregation may progress in the slurry manufacturing process, which may deteriorate the workability of the slurry spraying process. However, since the aggregation is suppressed by using a non-aqueous solvent that does not contain water as the solvent, the workability of the slurry spraying process can be improved.

  Further, since the alcohol-based dispersant is added to the slurry 20, the alcohol-based dispersant is added to the slurry 20, so that the metal oxide O powder can be dispersed and quick-drying can be achieved. Therefore, the workability after the slurry spraying process can be improved.

Note that the operation procedure shown in the above-described embodiment, various shapes and combinations of the constituent members, and the like are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.
For example, in the above-described embodiment, the inner space 12 of the mold 10 has a casting space for the turbine blades, but other parts may be used.
The crucible 1 and the mold 10 are not necessarily used as a set, and may be used alone.

DESCRIPTION OF SYMBOLS 1 ... Crucible 2,12 ... Internal space 3 ... Partition 3a ... Base layer 3b ... Coating layer 3b ... Coating layer 10 ... Mold 20 ... Slurry C ... Ceramics G ... Spray gun O ... Metal oxide

Claims (8)

A casting tool used for precision casting of a TiAl-based alloy,
A partition wall defining an internal space capable of storing the molten TiAl-based alloy;
The partition includes a base layer formed of ceramics,
A coating layer that is formed of a metal oxide having a stronger bond with oxygen than the ceramic, and coats the base layer on the inner space side;
I have a,
The said base layer is formed of 99% or more of zirconia, The casting tool characterized by the above-mentioned .   The casting tool according to claim 1, wherein the metal oxide is any one of yttrium oxide, ytterbium oxide, and erbium oxide.   The casting tool according to claim 1 or 2, wherein the coating layer has a thickness of 0.08 mm to 0.48 mm. A method for producing a casting tool according to any one of claims 1 to 3 ,
A slurry production step of producing a slurry by mixing the metal oxide powder and a solvent;
And a slurry spraying step of spraying the slurry on the inner space side of the base layer. The method for producing a casting tool according to claim 4 , wherein the powder has a particle size of 0.5 μm or more and 3 μm or less. The said solvent is a non-aqueous solvent which does not contain water, The production method of the casting tool of Claim 4 or 5 characterized by the above-mentioned. The method for producing a casting tool according to any one of claims 4 to 6 , wherein an alcohol-based dispersant is added to the slurry.   A precision casting method using the casting tool according to any one of claims 1 to 3.

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